The present invention relates generally to web handling and processing equipment and, more particularly, to an apparatus for decurling laminated composite webs.
Laminated composite webs having a relatively thin film layer adhered to a relatively thick paper layer and laminators for forming such webs are described in U.S. Pat. No. 4,254,173 of Peer and U.S. Pat. No. 4,572,752 of Jensen et al., which are both hereby specifically incorporated by reference for all that is disclosed therein. A laminated composite web such as described in the above patents is wound on a takeup spool after emerging from a production laminator. The direction of winding of the spool is usually such that the film layer of the composite web is positioned inwardly of the paper layer. The laminated composite web is stored in this spool form. Due to the fact that the film portion of the composite is ordinarily still warm and readily deformable after emerging from the laminator, the film portion of the composite "takes a set" while it is positioned on the windup spool such that the film layer is slightly shrunk with respect to the exposed portion of the paper layer due to its more radially inward location on the spool. The paper layer of the web, which is much thicker than the film layer, takes a differential type of set with the thickness portion of the paper web positioned adjacent the film web being slightly shrunk relative the thickness portion of the paper web that is positioned most remotely from the film web. As a result, a length of composite, upon being unwound from the spool, tends to curl up with the film side of the composite positioned on the inside of the curl. Curling of the composite web in this manner causes problems with other operations subsequently performed on the composite web such as die cutting. As a result, it is desirable to decurl the composite web before preforming these further operations.
It is known in the paper-treating arts that paper will shorten each time it goes through a cycle of having moisture applied to it and then removed from it, i.e. after the completion of such a cycle the paper will be shorter than its previous length even when the paper moisture content after the cycle is returned to the original value. This phenomenon is known in the art as "moisture hysteresis". In prior art paper web decurling units used on pure paper webs, a decurling roll which has a surface that transports moisture to the surface of the paper web passing thereover is used to add moisture to one side (the long side) of a curled paper web. During subsequent air drying of the paper web, the paper on the side to which moisture was applied is relative shrunk, while the other side of the paper web remains of a relatively constant length.